1. Field of the Invention
The present invention relates to the structure of a polishing head for a CMP apparatus configured to planarize a wafer plane evenly throughout the wafer plane, a CMP apparatus that includes the polishing head, and a semiconductor integrated circuit manufacturing method using the CMP polishing apparatus.
2. Description of the Related Art
In recent years, new microfabrication technologies have been developed as the level of integration and performance of semiconductor integrated circuits (hereinafter abbreviated as LSIs) has increased. Chemical mechanical polishing (hereinafter abbreviated as CMP) is one of the new technologies, and is used frequently in LSI manufacturing processes, in particular, steps included in a multi-layer wiring forming process which are the planarizing of an interlayer insulating film, the forming of a metal plug, and the forming of embedded wiring. The basic structure of CMP apparatus includes a rotating platen to which a polishing pad is stuck, a wafer holding head, and a slurry feeding nozzle, and a pad renewing device (a conditioner) is further included. The polishing pad side is not always the rotating platen. There are cases where the CMP apparatus includes a plurality of pads for one head, and then there are the opposite cases where the CMP apparatus includes a plurality of heads for one pad. Parameters for controlling CMP apparatus include, other than the method of polishing, polishing load, the rotation speed of the platen, the rotation speed of the head, the method of selecting and feeding slurry, the conditions and frequency of conditioning, and the like. One way to control CMP apparatus is pressurizing an airbag against a head portion to which a wafer is fixed as illustrated in FIG. 13 (see, for example, Japanese Patent Application Laid-open No. 2005-268566).
However, the head structure disclosed in Japanese Patent Application Laid-open No. 2005-268566 in which a wafer is fixed through pressurization with the use of an air bag has the following inconveniences. Specifically, the pressure from the pressurized air bag is locally high along a peripheral portion of the air bag, and an wafer region that is in contact with that portion is pressed to the polishing pad more firmly than other wafer regions, which means that more polishing target insulating material is polished off than in other wafer regions. With too much polishing target insulating material polished off in a partial region of the wafer, the degree of polishing is uneven throughout the wafer plane, and the film thickness of the insulating material is fluctuated throughout the wafer plane as a result. Wafer regions where the film thickness is fluctuated have electrical characteristics fluctuations, which may cause anomaly in electrical characteristics.
FIG. 14 is a schematic diagram of the film fluctuations. As illustrated in FIG. 14, compressed air is introduced in the related art in order to press down a wafer 1, and high pressure 6 higher than the pressure in a central portion of the air bag applies locally to a peripheral portion of the air bag. In the portion of the wafer 1 that is pressed down from above by the high pressure portion, the rate of insulating film polishing rises in a high pressurization region X, where the pressure is intense, and more insulating film is polished off than in the central portion where the wafer 1 is pressed under less pressure. This lowers the in-plane evenness in the high pressurization region X of the wafer 1 after the planarizing of the insulating film material.